You can work on preventing French expansion, it's not like the Netherlands could've prevented France from taking the territory without outside help either.
That's a good point. There were no good options for protecting the Southern Netherlands so I don't know that Britain would be opposed to Austrian rule, if for some reason Austria had wanted to return.
The Netherlands was weak and an economic wreck in 1815 after enduring the Continental System. Its army was distrusted because of the high proportion of former Napoleonic officers and men. Even the stability of the restored House of Orange was an unknown quality and Britain's plan to marry the Prince of Orange to the Princess of Wales fell through fairly quickly.
The solution was to build the "Wellington Barrier", an extremely expensive line of forts that looked backwards to the situation of a century earlier, which itself had never really worked. The money was found and the forts built, but nobody was ever able to resolve the problem of manning them, since the Netherlands couldn't afford nearly such a large army. The best that could be worked out was a plan that hoped Prussian troops could move in quickly in an emergency.
Of course the whole system fell apart in 1830 when the Belgians decided they didn't like being part of the Netherlands anyway. It's hard to imagine Austria being less effective in keeping the area out of French hands.